Mac Pro – Does Mac Pro 2013 Support 5 GHz Wi-Fi?

No the first Mac Pro with a USB 3 port is the latest (6.1, late 2013)

From the specifications for your particular Mac Pro:

Connections and audio

• Four FireWire 800 ports (two on front panel, two on back panel)
• Five USB 2.0 ports (two on front panel, three on back panel)
• Two USB 2.0 ports on included keyboard
• Front-panel headphone minijack and internal speaker
• Optical digital audio input and output TOSLINK ports
• Analog stereo line-level input and output minijacks
• Multichannel audio through Mini DisplayPort

A quick Google search shows several PCI Express USB 3.0 cards, e.g.,

• Sonnet Allegro USB 3.0 PCIe
• CalDigit SuperSpeed PCI Express Card
• HighPoint RocketU card

The boot chime is always as loud as the volume when you turn off your mac. There are tools for mac to disable it I believe. I don't know wether those affect windows as well.

EDIT: It seems the volume you set in windows has no control over the volume when booting again. So if you only use windows anyhow, boot into Mac OS (by holding the alt-key when booting). Then set the volume to zero (turn it down, don't use the mute key). You're Mac shouldn't chime anymore.